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java.lang.Objectorg.apache.commons.collections4.map.AbstractIterableMap<K,V>
org.apache.commons.collections4.map.AbstractMapDecorator<K,V>
org.apache.commons.collections4.map.LazyMap<K,V>
public class LazyMap<K,V>
Decorates another Map
to create objects in the map on demand.
When the get(Object)
method is called with a key that does not
exist in the map, the factory is used to create the object. The created
object will be added to the map using the requested key.
For instance:
Factory<Date> factory = new Factory<Date>() { public Date create() { return new Date(); } } Map<String, Date> lazy = LazyMap.lazyMap(new HashMap<String, Date>(), factory); Date date = lazy.get("NOW");After the above code is executed,
date
will refer to
a new Date
instance. Furthermore, that Date
instance is mapped to the "NOW" key in the map.
Note that LazyMap is not synchronized and is not thread-safe.
If you wish to use this map from multiple threads concurrently, you must use
appropriate synchronization. The simplest approach is to wrap this map
using Collections.synchronizedMap(Map)
. This class may throw
exceptions when accessed by concurrent threads without synchronization.
This class is Serializable from Commons Collections 3.1.
Nested Class Summary |
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Nested classes/interfaces inherited from interface java.util.Map |
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Map.Entry<K,V> |
Field Summary | |
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protected Transformer<? super K,? extends V> |
factory
The factory to use to construct elements |
Constructor Summary | |
---|---|
protected |
LazyMap(Map<K,V> map,
Factory<? extends V> factory)
Constructor that wraps (not copies). |
protected |
LazyMap(Map<K,V> map,
Transformer<? super K,? extends V> factory)
Constructor that wraps (not copies). |
Method Summary | ||
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V |
get(Object key)
|
|
static
|
lazyMap(Map<K,V> map,
Factory<? extends V> factory)
Factory method to create a lazily instantiated map. |
|
static
|
lazyMap(Map<K,V> map,
Transformer<? super K,? extends V> factory)
Factory method to create a lazily instantiated map. |
Methods inherited from class org.apache.commons.collections4.map.AbstractMapDecorator |
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clear, containsKey, containsValue, decorated, entrySet, equals, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values |
Methods inherited from class org.apache.commons.collections4.map.AbstractIterableMap |
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mapIterator |
Methods inherited from class java.lang.Object |
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clone, finalize, getClass, notify, notifyAll, wait, wait, wait |
Methods inherited from interface java.util.Map |
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clear, containsKey, containsValue, entrySet, equals, hashCode, isEmpty, keySet, put, putAll, remove, size, values |
Field Detail |
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protected final Transformer<? super K,? extends V> factory
Constructor Detail |
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protected LazyMap(Map<K,V> map, Factory<? extends V> factory)
map
- the map to decorate, must not be nullfactory
- the factory to use, must not be null
IllegalArgumentException
- if map or factory is nullprotected LazyMap(Map<K,V> map, Transformer<? super K,? extends V> factory)
map
- the map to decorate, must not be nullfactory
- the factory to use, must not be null
IllegalArgumentException
- if map or factory is nullMethod Detail |
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public static <K,V> LazyMap<K,V> lazyMap(Map<K,V> map, Factory<? extends V> factory)
K
- the key typeV
- the value typemap
- the map to decorate, must not be nullfactory
- the factory to use, must not be null
IllegalArgumentException
- if map or factory is nullpublic static <V,K> LazyMap<K,V> lazyMap(Map<K,V> map, Transformer<? super K,? extends V> factory)
K
- the key typeV
- the value typemap
- the map to decorate, must not be nullfactory
- the factory to use, must not be null
IllegalArgumentException
- if map or factory is nullpublic V get(Object key)
get
in interface Map<K,V>
get
in interface Get<K,V>
get
in class AbstractMapDecorator<K,V>
Map.get(Object)
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